1. Field of the Invention
The present invention relates to a sheet feeding apparatus for feeding sheets one by one, and more particularly, it relates to a sheet feeding apparatus used with a recording apparatus such as a copying machine, a printer and the like.
2. Related Background Art
In the past, there has been proposed a sheet feeding apparatus used with a recording apparatus such as a copying machine, a printer and the like, in which, for example, sheets are fed out one by one by means of a semi-circular feed roller one rotation of which is controlled, and the fed sheet is supplied to a recording portion by a convey roller. The feed roller is provided with a flag in order to stop the feed roller after one rotation, and, by detecting the flag by a sensor (photo-interrupter or the like), completion of one rotation of the feed roller is detected. Further, in a drive system, a driving force of a convey roller rotatable normally and reversely is switched by a pendulum gear to effect connection or disconnection of transmission of the driving force. That is to say, when the convey roller is rotated in a normal direction, the driving force is transmitted to the feed roller by the pendulum gear; whereas, when the convey roller is rotated in a reverse direction, the transmission of the driving force is released. Incidentally, in the released position, a slide lever can be fitted into a support member of the pendulum gear to fixedly keep the posture of the gear, and, when the convey roller is rotated in the normal direction, only the convey roller can be rotated. The slide lever is disengaged from the support member of the pendulum gear when a carriage on which a recording head is mounted is shifted up to an end of the apparatus, with the result that the pendulum gear can freely be moved. In the condition that the fixing of the pendulum gear is released, when the convey roller is rotated in the normal direction, the feed roller is rotated together with the convey roller.
In a fundamental flow of the sheet in the sheet feeding, first of all, the carriage is shifted up to the end of the apparatus to rotate the convey roller and the feed roller, thereby feeding out a single sheet. When the completion of one rotation of the feed roller is detected by the sensor, the convey roller is rotated in the reverse direction by a predetermined amount, thereby releasing the transmission of the driving force to the feed roller. Here, when the carriage is returned toward a center of the apparatus, the slide lever is fitted into the support member of the pendulum gear to fix the posture of the gear, and only the convey roller is rotated, with the result that the sheet is conveyed to the recording portion only by the convey roller.
However, due to dispersion in sheet features, since a time period from when the rotation of the feed roller is started to when a leading edge of the sheet reaches a sheet leading edge detecting sensor (referred to as "PE sensor" hereinafter) is varied from sheet to sheet, when one rotation of the feed roller is completed, a distance from the convey roller (sheet leading edge detecting sensor) to the leading edge of the sheet is also varied from sheet to sheet. Thus, a dispersion correcting operation, i.e., a feeding operation of the leading edge to an initial position in which, as shown in FIGS. 9A to 9D, after one rotation of the feed roller is completed, the sheet is set at an image leading portion recording position by reverse and normal rotations of the convey roller is required.
In FIGS. 9A to 9D, "P" indicates the sheet; 100 denotes the convey roller; 101 denotes the PE sensor (sheet leading edge detecting sensor); and 102 denotes the recording head. Further, ".beta." indicates a normal convey distance of the sheet P from when the leading edge of the sheet is detected by the PE sensor 101 to when one rotation of the feed roller is completed; ".epsilon." indicates a distance from the PE sensor 101 to a recording position of the recording head 102; ".gamma." indicates a reverse rotation amount required for the above-mentioned drive switching; ".sigma." indicates a backlash correction amount when the normal rotation is effected again; ".delta.1" indicates a blank amount from the leading edge of the sheet to a leading portion of a record permitting area; and ".delta.2" indicates a blank amount from the leading portion of the record permitting area to an image leading end portion based upon image data.
FIG. 9A shows a condition that the sheet P is fed out by the distance .beta. after one rotation of the feed roller was completed. FIG. 9B shows a condition that the sheet is returned by rotating the convey roller reversely by an amount corresponding to by the sum of the reverse rotation amount .gamma. required for the drive switching, an excessive fed amount in FIG. 9A and the backlash correction amount .sigma. of the drive switching portion. In this case, the reverse rotation amount of the convey roller is defined as (.beta.-.epsilon.+.sigma.-.delta.1), and diameters of the rollers are designed so that this reverse rotation amount becomes greater than the reverse rotation amount .gamma. required for the drive switching without fail. FIG. 9C shows a condition that the sheet is fed out by rotating the convey roller in the normal direction by the backlash correction amount .sigma.. As a result, the leading portion of the record permitting area is fed to the recording position (record starting position) of the recording head. FIG. 9D shows a condition that the sheet is fed out by rotating the convey roller in the normal direction by the blank amount .delta.2 with reference to the blank amount .delta.2 to the image leading portion based upon the image data. From this condition, the recording is started.
However, in the above-mentioned conventional apparatus, as mentioned above, since the leading edge of the sheet is returned up to the recording position of the recording head and then is fed out by the blank amount regardless of the image data, the shifting amount and time of the sheet required for the heading to the recording position become great, thereby worsening the record processing speed of the recording apparatus.
Concretely, for example, when .beta.=20 mm, .epsilon.=8 mm, .gamma.=5 mm, .sigma.=1 mm, .delta.1=2 mm and .delta.2=4 mm, the shifting amount of the sheet required for the heading will be (.beta.-.epsilon.+.sigma.-.delta.1+.sigma.-.delta.2)=16 mm.